The delivery of a drug by inhalation allows deposition of the drug in different sections of the respiratory tract, e.g., throat, trachea, bronchi and alveoli. Generally, the smaller the particle size, the longer the particle will remain suspended in air and the farther down the respiratory tract the drug can be delivered. Corticosteroids are delivered by inhalation using nebulizers, metered dose inhalers, or dry powder inhalers. The principle advantages of nebulizers over other methods of pulmonary installation are that patient cooperation is not required and the delivery of higher doses of medication is easier. The main concerns about nebulizers, however, are their increased cost, reduced portability and the inconvenience of needing to prepare medication beforehand and the increased time requirement for administering a treatment. A method of improving the administration of drugs, such as corticosteroids by nebulization would be desired.
Budesonide ((R,S)-11β, 16α, 17, 21-tetrahydroxypregna-1, 4-diene-3, 20-dione cyclic 16, 17-acetal with butyraldehyde; C25H34O6; Mw: 430.5) is well known. It is provided commercially as a mixture of two isomers (22R and 22S). Budesonide is an anti-inflammatory corticosteroid that exhibits potent glucocorticoid activity. Administration of budesonide is indicated for maintenance treatment of asthma and as prophylactic therapy in children.
Commercial formulations of budesonide are sold by AstraZeneca LP (Wilmington, Del.) under the trademarks ENTOCORT™ EC, PULMICORT RESPULES®, Rhinocort Aqua®, Rhinocort® Nasal Inhaler and Pulmicort Turbuhaler®, and under its generic name. PULMICORT RESPULES® suspension, which is a sterile aqueous suspension of micronized budesonide, is administered by inhalation using a nebulizer, in particular a compressed air driven jet nebulizer that delivers from 2 to 18% of the drug mass contained in the nominal charge. The general formulation for a unit dose of the PULMICORT RESPULES is set forth in U.S. Pat. No. 6,598,603, and it is an aqueous suspension in which budesonide is suspended in an aqueous medium comprising about 0.05 to 1.0 mg of budesonide, 0.05 to 0.15 mg of NaEDTA, 8.0 to 9.0 mg of NaCl, 0.15 to 0.25 mg of polysorbate, 0.25 to 0.30 mg of anhydrous citric acid, and 0.45 to 0.55 mg of sodium citrate per one ml of water. RHINOCORT® NASAL INHALER™ is a metered-dose pressurized aerosol unit containing a suspension of micronized budesonide in a mixture of propellants. RHINOCORT® AQUA™ is an unscented metered-dose manual-pump spray formulation containing a suspension of micronized budesonide in an aqueous medium. The suspensions should not be administered with an ultrasonic nebulizer.
A wide variety of nebulizers differing in mode of operation are available, e.g. jet nebulizers (optionally sold with compressors), ultrasonic nebulizers, vibrating membrane, vibrating mesh nebulizers, vibrating plate nebulizers, vibrating cone nebulizers, and others. The vibrating mesh, vibrating cone or vibrating plate nebulizers are of particular interest since they do not require the use of an air compressor for delivery, have a minimal residual volume in the reservoir after delivery of a unit dose, and can be used to deliver low volumes of inhalable solutions. Exemplary vibrating membrane, mesh or plate nebulizers are described by R. Dhand (Respiratory Care, (December 2002), 47(12), p. 1406-1418). Keller et al. (ATS 99th International Conference, Seattle, May 16-21, 2003; poster 2727) disclose the results of a study on the administration of AZTREONAM with a PARI eFlow nebulizer and report low oropharyngeal deposition, nebulization efficiency unaffected by fill volume, a respirable fraction of 82±1.7%, constant dose administration per inhalation cycle time, and an excellent correlation between delivered dose, fill volume and nebulization time, and expected high lung deposition.
The desired properties of a liquid for nebulization generally include: 1) reduced viscosity; 2) sterile medium; 3) reduced surface tension; 4) stability toward the mechanism of the nebulizer; 5) moderate pH of about 4-10; 6) ability to form droplets with an MMAD of <5 μm or preferably <3 μm; 7) absence of irritating preservatives and stabilizing agents; 8) suitable tonicity. On the one hand, suspensions possess some advantages but on the other hand solutions possess other advantages.
Smaldone et al. (J. Aerosol Med. (1998), 11, 113-125) disclose the results of a study on the in vitro determination of inhaled mass and particle distribution of a budesonide suspension. They conclude that 2%-18% of the nebulizer's charge of budesonide was delivered from the suspension, meaning that budesonide delivery was incomplete resulting in a significant waste of drug. In the thirteen most efficient systems, the suspension can be nebulized sufficiently well for lower respiratory tract delivery.
Another study further demonstrated the highly variable efficiency of nebulization from one nebulizer to another. Barry et al. (J. Allergy Clin. Immunol. (1998), 320-321) state that this variability should be taken into account when treating patients with nebulized budesonide. Berg et al. (J. Aerosol Sci. (1998), 19(7), 1101-1104) also report the highly variable efficiency of nebulization of PULMICORT™ suspension from one nebulizer to the next. Moreover, the mass mean aerodynamic diameter (MMAD) of the nebulized droplets is highly variable from one nebulizer to the next. In general, suspensions are less efficiently nebulized than solutions, O'Riordan (Respiratory Care, (2002), 1305-1313). Inhaled corticosteroids are utilized in the treatment of asthma and are of significant benefit because they are delivered directly to the site of action, the lung. The goal of an inhaled corticosteroid is to provide localized therapy with immediate drug activity in the lungs. Inhaled corticosteroids are well absorbed from the lungs. In fact, it can be assumed that all of the drug available at the receptor site in the lungs will be absorbed systemically. However, it is well known that using current methods and formulations the greater part of an inhaled corticosteroid dose is swallowed and becomes available for oral absorption, resulting in unwanted systemic effects. For inhaled corticosteroids, high pulmonary availability is more important than high oral bioavailability because the lung is the target organ. A product with high pulmonary availability has greater potential to exert positive effects in the lung. The ideal inhaled corticosteroid formulation would provide minimum oral delivery thereby reducing the likelihood of systemic adverse effects.
The majority of the corticosteroid dose delivered to the lung is absorbed and available systemically. For the portion of the inhaled corticosteroid dose delivered orally, bioavailability depends upon absorption from the GI tract and the extent of first pass metabolism in the liver. Since this oral component of corticosteroid drug delivery does not provide any beneficial therapeutic effect but can increase systemic side effects, it is desirable for the oral bioavailability of inhaled corticosteroid to be relatively low.
Both particle size and formulation influence the efficacy of an inhaled corticosteroid. The formulation of a drug has a significant impact on the delivery of that drug to the lungs, and therefore its efficacy. Most important in the delivery of drug to the lung are the aerosol vehicle and the size of the particles delivered. Additionally, a reduced degree of pulmonary deposition suggests a greater degree of oropharyngeal deposition. Due to a particular formulation employed, some corticosteroids are more likely to be deposited in the mouth and throat and may cause local adverse effects.
While receptor distribution is the major determinant of bronchodilator efficacy, particle size appears to be more important in determining the efficacy of an inhaled corticodsteroid. The smallest airways have an internal diameter of 2 micrometers (mcm) or less. Thus, an inhaler with particles having a mean aerodynamic diameter of 1 mcm should have a greater respirable fraction than an inhaler with particles that have an average diameter of 3.5 to 4 mcm. For patients with obstructive lung disease, all particles should ideally be no greater than 2 to 3 mcm. A particle that is small (less than 5 mcm) is more likely to be inhaled into the smaller airways of the lungs, thus improving efficacy. In contrast, particles that are larger than 5 mcm can be deposited in the mouth and throat, both reducing the proportion of particles that reach the lungs and potentially causing local adverse effects such as oral candidiasis and hoarseness (dysphonia). Particles having a mass median aerodynamic diameter (MMAD) of close to 1 mcm are considered to have a greater respirable fraction per dose than those with a diameter of 3.5 mcm or greater.
A further disadvantage to the nebulization of budesonide suspensions is the need to generate very small droplets, MMDD of about <3 μm. Since the nebulized droplets are so small, then the micronized budesonide must be even smaller or in the range of 0.5-2.0 μm and the particles should have a narrow particle size distribution. Generation of such particles is difficult.
Even so, efforts have been made to improve the nebulization of budesonide suspensions with ultrasonic nebulizers by using submicron-sized particles (Keller et al. in Respiratory Drug Delivery VIII (2002), 197-206). A suspension of nanoparticles (0.1-1.0 μm) of the corticosteroid might be used to increase the proportion of respirable particles as compared to a coarser suspension as in the PULMICORT™ suspension. No improvement over PULMICORT™ suspension (about 4.4 μm budesonide particle size in suspension) was observed. Moreover, concerns exist regarding the use of nanosuspensions in that the small particles (<0.05 μm) may induce an allergic response in a subject. Sheffield Pharmaceuticals, Inc. (St. Louis, Mo.; “The Pharmacokinetics of Nebulized Nanocrystal Budesonide Suspension in Healthy Volunteers”, Kraft, et al. in J. Clin. Pharmacol., (2004), 44:67-72) has disclosed the preparation and evaluation of UDB (unit dose budesonide), which is a suspension-based formulation containing nanoparticles of budesonide dispersed in a liquid medium. This product is being developed by MAP Pharmaceuticals, Inc. (Mountain View, Calif.). Seeman et al. (ATS 99th International Conference, Seattle, May 16-21, 2003; poster 2727) disclose the results of a study evaluating the performance of the PARI eFlow nebulizer with a budesonide suspension (PULMICORT RESPULES, 500 μg/ml, in a 2 ml ampoule) and report achieving a MMAD of 3.6-4.2 μm and a respirable fraction of greater than 67%.
The inhalation of drug particles as opposed to dissolved drug is known to be disadvantageous. Brain et al. (Bronchial Asthma, 2nd Ed. (Ed. E. B. Weis et al., Little Brown & Co. (1985), pp. 594-603) report that less soluble particles that deposit on the mucous blanket covering pulmonary airways and the nasal passages are moved toward the pharynx by the cilia. Such particles would include the larger drug particles deposited in the upper respiratory tract. Mucus, cells and debris coming from the nasal cavities and the lungs meet at the pharynx, mix with saliva, and enter the gastrointestinal tract upon being swallowed. Reportedly, by this mechanism, particles are removed from the lungs with half-times of minutes to hours. Accordingly, there is little time for solubilization of slowly dissolving drags, such as budesonide. In contrast, particles deposited in the nonciliated compartments, such as the alveoli, have much longer residence times. Since it is difficult to generate very small particles of budesonide for deep lung deposition, much of the inhaled suspension would likely be found in the upper to middle respiratory tract. However, it is much easier to generate small droplets from a solution than it is from a suspension of solids. For these reasons, nebulization of a budesonide-containing solution should be preferred over that of a suspension.
O'Riordan (Respiratory Care (2002 November), 47(11), 1305-1313) states that drugs can be delivered by nebulization of either solutions or suspensions, but that in general, nebulization of a solution is preferred over that of a suspension. He states that ultrasonic nebulizers should not be used on suspensions and should be used only on solutions.
O'Callaghan (Thorax, (1990), 45, 109-111), Storr et al. (Arch. Dis. Child (1986), 61, 270-273), and Webb et al. (Arch. Dis. Child (1986), 61, 1108-1110) suggest that nebulization of corticosteroid (in particular beclomethasone) solutions may be preferred over that of suspensions because the latter may be inefficient if the nebulized particles are too large to enter the lung in therapeutically effective amounts. However, data presented by O'Callaghan (J. Pharm. Pharmacol. (2002), 54, 565-569) on the nebulization of flunisolide solution versus suspension showed that the two performed similarly. Therefore, it cannot be generalized that nebulization of a solution is preferred over that of a suspension.
Accordingly, there is a widely recognized need for a non-suspension formulation comprising a corticosteroid for administration via nebulization. However, the PULMICORT® suspension unit dose formulation is widely available and accepted in the field of inhalation therapy. It would be of great benefit to this field of therapy to provide a method of improving the administration of the PULMICORT® suspension unit dose formulation, or more generally, of a suspension unit dose formulation containing a corticosteroid.
However, the current focus in nebulizer therapy is to administer higher concentrations of drug, use solution, preferably predominantly aqueous-based solutions in preference to non-aqueous or alcoholic or non-aqueous alcoholic solutions or suspensions if possible, minimize treatment time, synchronize nebulization with inhalation, and administer smaller droplets for deeper lung deposition of drug.
Corticosteroid-containing solutions for nebulization are known. There are a number of different ways to prepare solutions for nebulization. These generally have been prepared by the addition of a cosolvent, surfactant, or buffer. However, cosolvents, such as ethanol, polyethylene glycol and propylene glycol are only tolerated in low amounts when administered by inhalation due to irritation of the respiratory tract. There are limits to acceptable levels of these cosolvents in inhaled products. Typically, the cosolvents make up less than about 35% by weight of the nebulized composition, although it is the total dose of cosolvent as well as its concentration that determines these limits. The limits are set by the propensity of these solvents either to cause local irritation of lung tissue, to form hyperosmotic solutions that would draw fluid into the lungs, and/or to intoxicate the patient. In addition, most potential hydrophobic therapeutic agents are not sufficiently soluble in these cosolvent mixtures.
Saidi et al. (U.S. Pat. No. 6,241,969) disclose the preparation of corticosteroid-containing solutions for nasal and pulmonary delivery. The dissolved corticosteroids are present in a concentrated, essentially non-aqueous form for storage or in a diluted, aqueous-based form for administration.
Keller et al. (in Respiratory Drug Delivery IX (2004) 221-231) disclose the deposition of solution formulations containing budesonide and surfactants to children.
Lintz et al. (AAPS Annual Meeting and Exposition, Baltimore, Nov. 8, 2004; Poster M1128) disclose the preparation and aerosol characterization of liquid formulations containing budesonide, water, citrate salt, sodium chloride and alcohol, propylene glycol and/or surfactant, such as Tween, Pluronic, or phospholipids with HLB-values between 10 and 20. The aerosol characterization of such a combination surfactant solution in a vibrating membrane/mesh nebulizer (the Pari eFlow) compared to a suspension was studied using adult and child breath simulation. They reported a respirable fraction of 83.3% for the PARI eFlow with the solution and 61% for the PULMICORT RESPULES with the PARI LC+. They also reported the results regarding the respirable drug delivery rate (% drug <5 μm/min), delivered dose (% of drug charged to device), drug delivery rate (% drug/min), and respirable dose (%<5 μm).
Schueepp et al. (ATS 99th International Conference, Seattle, May 16-21, 2003; poster 1607) disclose assessment of the aerosol performance of a customized eFlow Baby Functional Model with an experimental budesonide solution (100 μg in 0.5 ml) utilizing a baby cast model and applying different breathing patterns.
An alternative approach to administration of the PULMICORT™ suspension is administration of a liposome formulation. Waldrep et al. (J. Aerosol Med. (1994), 7(2), 135-145) reportedly succeeded in preparing a liposome formulation of budesonide and phosphatidylcholine derivatives.
None of the above-identified formulations has provided a method of improving the administration of a suspension-based unit dose formulation containing a corticosteroid. Instead, the general focus of the art has been to completely circumvent formulating a suspension by first preparing a liquid formulation that is then divided into multiple unit doses that are packaged for marketing and then sold for use.
Solubilization of drugs by cyclodextrins and their derivatives is well known. Cyclodextrins are cyclic carbohydrates derived from starch. The unmodified cyclodextrins differ by the number of glucopyranose units joined together in the cylindrical structure. The parent cyclodextrins contain 6, 7, or 8 glucopyranose units and are referred to as α-, β-, and γ-cyclodextrin respectively. Each cyclodextrin subunit has secondary hydroxyl groups at the 2 and 3 positions and a primary hydroxyl group at the 6-position. The cyclodextrins may be pictured as hollow truncated cones with hydrophilic exterior surfaces and hydrophobic interior cavities. In aqueous solutions, these hydrophobic cavities provide a haven for hydrophobic organic compounds that can fit all or part of their structure into these cavities. This process, known as inclusion complexation, may result in increased apparent aqueous solubility and stability for the complexed drug. The complex is stabilized by hydrophobic interactions and does not involve the formation of any covalent bonds.
This dynamic and reversible equilibrium process can be described by Equations 1 and 2, where the amount in the complexed form is a function of the concentrations of the drug and cyclodextrin, and the equilibrium or binding constant, Kb. When cyclodextrin formulations are administered by injection into the blood stream, the complex rapidly dissociates due to the effects of dilution and non-specific binding of the drug to blood and tissue components.
                              Drug          +          Cyclodextrin                ⁢                  ↔                      K            b                          ⁢        Complex                            Equation        ⁢                                  ⁢        1                                          K          b                =                              ⌊            Complex            ⌋                                              ⌊              Drug              ⌋                        ⁢                          ⌊              Cyclodextrin              ⌋                                                          Equation        ⁢                                  ⁢        2            
Binding constants of cyclodextrin and an active agent can be determined by the equilibrium solubility technique (T. Higuchi et al. in “Advances in Analytical Chemistry and Instrumentation Vol. 4”; C. N. Reilly ed.; John Wiley & Sons, Inc, 1965, pp. 117-212). Generally, the higher the concentration of cyclodextrin, the more the equilibrium process of Equations 1 and 2 is shifted to the formation of more complex, meaning that the concentration of free drug is generally decreased by increasing the concentration of cyclodextrin in solution.
The underivatized parent cyclodextrins are known to interact with human tissues and extract cholesterol and other membrane components, particularly upon accumulation in the kidney tubule cells, leading to toxic and sometimes fatal renal effects.
The parent cyclodextrins often exhibit a differing affinity for any given substrate. For example, γ-cyclodextrin often forms complexes with limited solubility, resulting in solubility curves of the type Bs. This behavior is known for a large number of steroids which imposes serious limitations towards the use of γ-CD in liquid preparations. β-CD, however, does not complex well with a host of different classes of compounds. It has been shown for β-DD and γ-CD that derivatization, e.g. alkylation, results in not only better aqueous solubility of the derivatives compared to the parent CD, but also changes the type of solubility curves from the limiting Bs-type to the more linear A-type curve (Bernd W. Muller and Ulrich Brauns, “Change of Phase-Solubility Behavior by Gamma-Cyclodextrin Derivatization”, Pharmaceutical Research (1985) p 309-310).
Chemical modification of the parent cyclodextrins (usually at the hydroxyls) has resulted in derivatives with improved safety while retaining or improving the complexation ability. Of the numerous derivatized cyclodextrins prepared to date, only two appear to be commercially viable: the 2-hydroxypropyl derivatives (HP-CD; neutral
